Description

The dig utility (domain information groper) is a flexible tool for interrogating
DNS name servers. It performs DNS lookups and displays the answers that
are returned from the name server(s) that were queried. Most DNS administrators
use dig to troubleshoot DNS problems because of its flexibility, ease of use
and clarity of output. Other lookup tools tend to have less functionality
than dig.

Although dig is normally used with command-line arguments, it also has a
batch mode of operation for reading lookup requests from a file. A
brief summary of its command-line arguments and options is printed when the
-h option is specified. Unlike earlier versions, the BIND 9 implementation of dig
allows multiple lookups to be issued from the command line.

Unless it is told to query a specific name server, dig tries
each of the servers listed in /etc/resolv.conf.

When no command line arguments or options are given, dig performs an
NS query for “.” (the root).

It is possible to set per-user defaults for dig with ${HOME}/.digrc. This
file is read and any options in it are applied before the
command line arguments.

The IN and CH class names overlap with the IN and CH
top level domains names. Either use the -t and -c options to
specify the type and class, or use "IN." and "CH." when looking
up these top level domains.

Simple Usage

The following is a typical invocation of dig:

dig @server name type

where:

server

The name or IP address of the name server to query. This can be an IPv4 address in dotted-decimal notation or an IPv6 address in colon-delimited notation. When the supplied server argument is a hostname, dig resolves that name before querying that name server. If no server argument is provided, dig consults /etc/resolv.conf and queries the name servers listed there. The reply from the name server that responds is displayed.

name

The name of the resource record that is to be looked up.

type

Indicates what type of query is required (ANY, A, MX, SIG, among others.) type can be any valid query type. If no type argument is supplied, dig performs a lookup for an A record.

Options

The following options are supported:

-4

Use only IPv4 transport. By default both IPv4 and IPv6 transports can be used. Options -4 and -6 are mutually exclusive.

-6

Use only IPv6 transport. By default both IPv4 and IPv6 transports can be used. Options -4 and -6 are mutually exclusive.

-baddress

Set the source IP address of the query to address. This must be a valid address on one of the host's network interfaces or 0.0.0.0 or ::. An optional port may be specified by appending: #<port>

-cclass

Override the default query class (IN for internet). The class argument is any valid class, such as HS for Hesiod records or CH for CHAOSNET records.

-ffilename

Operate in batch mode by reading a list of lookup requests to process from the file filename. The file contains a number of queries, one per line. Each entry in the file should be organized in the same way they would be presented as queries to dig using the command-line interface.

-h

Print a brief summary of command-line arguments and options.

-kfilename

Specify a transaction signature (TSIG) key file to sign the DNS queries sent by dig and their responses using TSIGs.

-m

Enable memory usage debugging.

-pport#

Query a non-standard port number. The port# argument is the port number that dig sends its queries instead of the standard DNS port number 53. This option tests a name server that has been configured to listen for queries on a non-standard port number.

-qname

Sets the query name to name. This can be useful in that the query name can be easily distinguished from other arguments.

-ttype

Set the query type to type, which can be any valid query type supported in BIND9. The default query type “A”, unless the -x option is supplied to indicate a reverse lookup. A zone transfer can be requested by specifying a type of AXFR. When an incremental zone transfer (IXFR) is required, type is set to ixfr=N. The incremental zone transfer will contain the changes made to the zone since the serial number in the zone's SOA record was N.

-xaddr

Simplify reverse lookups (mapping addresses to names ). The addr argument is an IPv4 address in dotted-decimal notation, or a colon-delimited IPv6 address. When this option is used, there is no need to provide the name, class and type arguments. The dig utility automatically performs a lookup for a name like 11.12.13.10.in-addr.arpa and sets the query type and class to PTR and IN, respectively. By default, IPv6 addresses are looked up using nibble format under the IP6.ARPA domain. To use the older RFC1886 method using the IP6.INT domain, specify the -i option. Bit string labels (RFC 2874) are now experimental and are not attempted.

-y [hmac:]name:key

Specify a transaction signature (TSIG) key on the command line. This is done to sign the DNS queries sent by dig, as well as their responses. You can also specify the TSIG key itself on the command line using the -y option. The optional hmac is the type of TSIG; the default is HMAC-MD5. The name argument is the name of the TSIG key and the key argument is the actual key. The key is a base-64 encoded string, typically generated by dnssec-keygen(1M).

Caution should be taken when using the -y option on multi-user systems, since the key can be visible in the output from ps(1) or in the shell's history file. When using TSIG authentication with dig, the name server that is queried needs to know the key and algorithm that is being used. In BIND, this is done by providing appropriate key and server statements in named.conf.

QUERY OPTIONS

The dig utility provides a number of query options which affect the
way in which lookups are made and the results displayed. Some of
these set or reset flag bits in the query header, some determine
which sections of the answer get printed, and others determine the timeout and
retry strategies.

Each query option is identified by a keyword preceded by a plus
sign (+). Some keywords set or reset an option. These may be
preceded by the string no to negate the meaning of that keyword.
Other keywords assign values to options like the timeout interval. They have
the form +keyword=value. The query options are:

+[no]tcp

Use [do not use] TCP when querying name servers. The default behaviour is to use UDP unless an AXFR or IXFR query is requested, in which case a TCP connection is used.

+[no]vc

Use [do not use] TCP when querying name servers. This alternate syntax to +[no]tcp is provided for backwards compatibility. The “vc” stands for “virtual circuit”.

+[no]ignore

Ignore truncation in UDP responses instead of retrying with TCP. By default, TCP retries are performed.

+domain=somename

Set the search list to contain the single domain somename, as if specified in a domain directive in /etc/resolv.conf, and enable search list processing as if the +search option were given.

+[no]search

Use [do not use] the search list defined by the searchlist or domain directive in resolv.conf (if any). The search list is not used by default.

+[no]showsearch

Perform [do not perform] a search showing intermediate results.

+[no]defname

Deprecated, treated as a synonym for +[no]search.

+[no]aaonly

Sets the aa flag in the query.

+[no]aaflag

A synonym for +[no]aaonly.

+[no]adflag

Set [do not set] the AD (authentic data) bit in the query. This requests that the server return, regardless of whether all of the answer and authority sections have all been validated as secure according to the security policy of the server. A setting of AD=1 indicates that all records have been validated as secure and the answer is not from an OPT-OUT range. AD=0 indicates that some part of the answer is insecure or not validated.

+[no]cdflag

Set [do not set] the CD (checking disabled) bit in the query. This requests the server to not perform DNSSEC validation of responses.

+[no]cl

Display [do not display] the CLASS when printing the record.

+[no]ttlid

Display [do not display] the TTL when printing the record.

+[no]recurse

Toggle the setting of the RD (recursion desired) bit in the query. This bit is set by default, which means dig normally sends recursive queries. Recursion is automatically disabled when the +nssearch or +trace query options are used.

+[no]nssearch

When this option is set, dig attempts to find the authoritative name servers for the zone containing the name being looked up and display the SOA record that each name server has for the zone.

+[no]trace

Toggle tracing of the delegation path from the root name servers for the name being looked up. Tracing is disabled by default. When tracing is enabled, dig makes iterative queries to resolve the name being looked up. It will follow referrals from the root servers, showing the answer from each server that was used to resolve the lookup.

+[no]cmd

Toggle the printing of the initial comment in the output identifying the version of dig and the query options that have been applied. This comment is printed by default.

+[no]short

Provide a terse answer. The default is to print the answer in a verbose form.

+[no]identify

Show [or do not show] the IP address and port number that supplied the answer when the +short option is enabled. If short form answers are requested, the default is not to show the source address and port number of the server that provided the answer.

+[no]comments

Toggle the display of comment lines in the output. The default is to print comments.

+[no]stats

Toggle the printing of statistics: when the query was made, the size of the reply and so on. The default behaviour is to print the query statistics.

+[no]qr

Print [do not print] the query as it is sent. By default, the query is not printed.

+[no]question

Print [do not print] the question section of a query when an answer is returned. The default is to print the question section as a comment.

+[no]answer

Display [do not display] the answer section of a reply. The default is to display it.

+[no]authority

Display [do not display] the authority section of a reply. The default is to display it.

+[no]additional

Display [do not display] the additional section of a reply. The default is to display it.

+[no]all

Set or clear all display flags.

+time=T

Sets the timeout for a query to T seconds. The default time out is 5 seconds. An attempt to set T to less than 1 will result in a query timeout of 1 second being applied.

+tries=T

Sets the maximum number of UDP attempts to T. The default number is 3 (1 initial attempt followed by 2 retries). If T is less than or equal to zero, the number of retries is silently rounded up to 1.

+retry=T

Sets the number of UDP retries to T. The default is 2.

+ndots=D

Set the number of dots that have to appear in name to D for it to be considered absolute. The default value is that defined using the ndots statement in /etc/resolv.conf, or 1 if no ndots statement is present. Names with fewer dots are interpreted as relative names and will be searched for in the domains listed in the search or domain directive in /etc/resolv.conf.

+bufsize=B

Set the UDP message buffer size advertised using EDNS0 to B bytes. The maximum and minimum sizes of this buffer are 65535 and 0 respectively. Values outside this range are rounded up or down appropriately.

+edns=#

Specify the EDNS version with which to query. Valid values are 0 to 255. Setting the EDNS version causes a EDNS query to be sent. +noedns clears the remembered EDNS version.

+[no]multiline

Print records like the SOA records in a verbose multi-line format with human-readable comments. The default is to print each record on a single line, to facilitate machine parsing of the dig output.

+[no]fail

Do not try the next server if you receive a SERVFAIL. The default is to not try the next server which is the reverse of normal stub resolver behavior.

+[no]besteffort

Attempt to display the contents of messages which are malformed. The default is to not display malformed answers.

+[no]dnssec

Request DNSSEC records be sent by setting the DNSSEC OK bit (DO) in the OPT record in the additional section of the query.

MULTIPLE QUERIES

The BIND 9 implementation of dig supports specifying multiple queries on the
command line (in addition to supporting the -f batch file option). Each
of those queries can be supplied with its own set of flags,
options and query options.

In this case, each query argument represent an individual query in the
command-line syntax described above. Each consists of any of the standard options
and flags, the name to be looked up, an optional query type,
and class and any query options that should be applied to that query.

A global set of query options, which should be applied to all
queries, can also be supplied. These global query options must precede the
first tuple of name, class, type, options, flags, and query options supplied
on the command line. Any global query options (except the +[no]cmd option) can
be overridden by a query-specific set of query options. For example:

dig +qr www.isc.org any -x 127.0.0.1 isc.org ns +noqr

...shows how dig could be used from the command line to make
three lookups: an ANY query for www.isc.org, a reverse lookup of 127.0.0.1
and a query for the NS records of isc.org. A global query
option of +qr is applied, so that dig shows the initial query it
made for each lookup. The final query has a local query option
of +noqr which means that dig will not print the initial query
when it looks up the NS records for isc.org.